Physics is so difficult to understand.

Underline the prepositional phrase, tell whether it is an adjective, adverb or a noun phrase.

The prepositional phrase in this sentence is "difficult to understand." It is an adjectival phrase because it gives information about a noun ("physics"), the subject of the sentence.

A prepositional phrase is either used to give information about a verb or a noun in the sentence. It must contain a preposition (like in, to, of, about, at, before, by, during, for, from, over, with, etc.), the object of the preposition, and possibly, words which modify the object.

It is an adjectival phrase if it modifies a noun (I can't reach the toy on the highest shelf.) It is an adverbial phrase if it modifies a verb (He approached with hesitation.) It is a noun phrase if it revolves around a subject, like a noun or pronoun (We come from various different backgrounds.)